原创 Tapestry的Cache组件

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有许多页面的一部分或者这个页面是很少更新的，他们通常是由外部文件来生成这个部分。所以我们可以把这部分内容cache住，当有新的请求时，我们就response cache，这样可以减少服务器的负担，还可以提高性能。其中oscache已经可以实现页面的cache和页面部分cache。oscache使用jsp tags来实现局部cache的。拿到Tapestry中肯定是行不通的。在同事的提醒下，想到写这个Tapestry的cache组件来达到重用的目的。

说干就干，先在头脑中想好要怎样使用cache（页面上的布局）。ok。 我想好了。

xml 代码

<span jwcid="@Cache" cacheProvider="ognl:cacheProvider" updateCondition="ognl:needUpdate">

    //Cache body, which is the content you want to cache.

span>

这里有2个参数，updateCondition 当为true时，我们就绕过cache， cacheProvider 我把他定义为一个接口，这样用户可以把cache存在任何地方。而且提供这样的一个接口，用户可以更好的操作cache。先看看jwc对cache组件的定义。

xml 代码

xml version="1.0" encoding="UTF-8"?>

  "-//Apache Software Foundation//Tapestry Specification 4.0//EN"
  "http://jakarta.apache.org/tapestry/dtd/Tapestry_4_0.dtd">

<component-specification allow-body="yes" allow-informal-parameters="no" class="com.live.spaces.dengyin2000.tapestry.tfancomponents.components.Cache">
    <description>
        Cache component, this component can inclue any content as its body, and cache its body.
        This is useful in rarely updated content.
    description>
    <parameter name="updateCondition" required="no" default-value="false">
        <description>
            The flag that need to refresh cache, it would casue tapestry render not use the cache.
        description>
    parameter>
    <parameter name="cacheProvider" required="yes">
        <description>
            You need to provider an cache provider to store its body content. for some simply use.
            Please see @com.live.spaces.dengyin2000.tapestry.tfancomponents.components.SimpleHtmlSourceCacheProvider
        description>
    parameter>
component-specification>

下面的是ICacheProvider接口：

java 代码

package com.live.spaces.dengyin2000.tapestry.tfancomponents.components;
/**
 * @author Denny - [email protected]
 * @since 2006-12-21
 */
public interface ICacheProvider {

    /**
     *
     * @param cacheKey
     * @param cacheContent
     */
    public void storeCache(String cacheKey, String cacheContent);

    /**
     *
     * @param cacheKey
     * @return
     */
    public String getCacheContent(String cacheKey);

    /**
     * This method provider to user, so that user can controll cache manaully.
     * @param cacheKey
     */
    public void removeCache(String cacheKey);

    /**
     * This method provider to user, so that user can controll cache manaully.
     * Clear all caches
     *
     */
    public void reset();

}

ok。 再来看看Cache组件的代码。

java 代码

package com.live.spaces.dengyin2000.tapestry.tfancomponents.components;

import java.io.PrintWriter;
import java.io.StringWriter;

import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
import org.apache.tapestry.AbstractComponent;
import org.apache.tapestry.IMarkupWriter;
import org.apache.tapestry.IRequestCycle;
import org.apache.tapestry.util.ContentType;

/**
 * @author Denny deng
 *
 */
public abstract class Cache extends AbstractComponent {

    protected static final Log logger = LogFactory.getLog(Cache.class);

    public abstract boolean getUpdateCondition();

    public abstract ICacheProvider getCacheProvider();

    @Override
    protected void renderComponent(IMarkupWriter writer, IRequestCycle cycle) {

        if (getUpdateCondition()){
            renderComponentWithCache(writer, cycle);
        }else{
            if (getCacheProvider().getCacheContent(this.getIdPath()) != null){

                //response cache html content.
                writer.printRaw(getCacheProvider().getCacheContent(this.getIdPath()));
            }else{
                renderComponentWithCache(writer, cycle);
            }
        }

    }

    private void renderComponentWithCache(IMarkupWriter writer, IRequestCycle cycle) {

        logger.debug("We need to refresh cache now.");
        CacheWriterWrapper cacheWrapper = new CacheWriterWrapper();
        super.renderBody(buildCacheMarkupWriter(cacheWrapper.getPrintWriter(), writer), cycle);
        String cacheContent = cacheWrapper.getCacheContent();
        logger.debug("fetched cache content, ready to put it into cache.");

        getCacheProvider().storeCache(this.getIdPath(), cacheContent);

        // response html content.
        writer.printRaw(cacheContent);
    }

    private IMarkupWriter buildCacheMarkupWriter(PrintWriter writer, IMarkupWriter sourceWriter){
        return this.getPage().getRequestCycle().getInfrastructure().getMarkupWriterSource().newMarkupWriter(writer, new ContentType(sourceWriter.getContentType()));
    }

    class CacheWriterWrapper{
        private StringWriter sw;
        private PrintWriter pw;
        public CacheWriterWrapper() {
            sw = new StringWriter();
            pw = new PrintWriter(sw);
        }

        public String getCacheContent(){
            return sw.getBuffer().toString();
        }

        public PrintWriter getPrintWriter(){
            return pw;
        }
    }
}

主要是得到cache组件body的内容，然后把body的内容cache住，下次的话就response Cache的内容。 其实也是满简单的。

我自己还写了一个简单CacheProvider。

java 代码

package com.live.spaces.dengyin2000.tapestry.tfancomponents.components;

import java.util.HashMap;
import java.util.Map;

/**
 * @author Denny - [email protected]
 * @since 2006-12-21
 */
public class SimpleHtmlSourceCacheProvider implements ICacheProvider {

    private Mapnew HashMap

    public String getCacheContent(String cacheKey) {
        return cache.get(cacheKey);
    }

    public void storeCache(String cacheKey, String cacheContent) {
        cache.put(cacheKey, cacheContent);
    }

    public void removeCache(String cacheKey) {
        cache.remove(cacheKey);
    }

    public void reset() {
        cache.clear();
    }
}

在使用中你可以把CacheProvider放到Global或者Visit对象中。注意要使用同一个CacheProvider。

 

我在google code host上面建了一个probject地址是http://code.google.com/p/tfancomponents/ 有兴趣的同学可以看看， 这是一个maven项目。